Conventionally, in a radio communication system, when a bit error rate of a receiving apparatus does not satisfy a predetermined value, there is generally performed an ARQ (Automatic Repeat reQuest) in which the receiving apparatus transmits a retransmission request signal to a transmitting apparatus and the transmitting apparatus transmits the same transmission data again according to this request.
Particularly, a packet transmission, which transmits data traffic, needs error control using ARQ since data transmission with no error must be ensured. In addition, the use of a hybrid ARQ (hereinafter referred to as HARQ) having an FEC (Forward Error Correction) function incorporated is standardized under 3GPP since occurrence of a packet error caused by a measurement error, control delay and the like is unavoidable even at the time of applying adaptive modulation and error correction where an optimal modulation system and a coding system are selected according to the state of a propagation path to improve throughput.
By the way, when the ARQ technique or HARQ technique is used in radio communication system of CDMA (Code Division Multiple Access) or OFDM-CDMA where CDMA and OFDM (Orthogonal Frequency Division Multiplexing) are combined, this is useful when propagation environments change at high speed, but provides a defect in which a large effect cannot be obtained when propagation environments change at low speed (in other words, a case in which the time variation of propagation environments is small).
In the CDMA, interference between spread codes occurs when there is a delay wave. The influence of interference between the spread codes differs for each spread code. In other words, there are a spread code where reception quality is largely degraded by interference and a spread code where reception quality is not degraded so much by interference.
For this reason, when the time variation of the propagation environments is small, transmission data transmitted using the spread code where reception quality is largely degraded still has poor reception quality on a receiving side even if retransmission is performed. Namely, regarding the symbol whose quality of line is poor at a first receiving time, the quality of line stays poor at second and the afterward receiving time for retransmission, and sufficient performance cannot be obtained even if the resultants are combined. As a result, there is a fear that only the reduction in transmission efficiency due to retransmission will be outstanding in addition to the point that improvement of the error rate of the received signal that should be originally obtained will not be obtained.